Video (rmvb) laggy when using WinAVI

[lazyturbo]

I have some .rmvb videos that I want to convert to mpeg. It seems like WinAVI is the only one out there that can do it pretty good.

But when I converted an rmvb, there are some parts where the video becomes laggy, and sometimes you can see blocks. I only saw this 2-3 times in a 40 minute video...but still, how do I fix this?

I tried using constant quality and constant video size. Constant video size makes the problem occur less, bit still exists.

[Krispy Kritter]

I've never that conversion myself, but it is usually better to not be reading AND writing to the same HD during video work.